P2000 G3 - Trespass Question

[WarNox]

Hi,

I'm looking at a P2000 G3 SAN where each controller had only 1 FC port (A1 and B1) plugged into an FC switch. One FC switch is now offline so there is only 1 path to each LUN, via Controller A. If I run 'show ports' I can indeed verify that only A1 has an 'Up' status.

Due to this I would expect that all LUNs should have trespassed to Contoller A, but if I run 'show vdisks' or view the vDisk status in the GUI I can see that the LUNs are still spread amongst both controllers.

Does the P2000 use ALUA (and is an active/active (SAA) array), so in this case IO is redirected from Controller A to Controller B without the need for LUN trespass?

The other thing I find strange is that the Hosts Map view has both A1 and B1 ports still listed for each volume, even though B1 is disconnected. Is this normal behaviour? Will this automatically update if I plug in A2 and B2?

Thanks for any help.

[Torsten.]

You will always see the configured mappings, no matter if a port is down or up.

Check if you see the default LUN owner vs. the current owner.

In case controller A cannot work, controller B will be at least the current owner.

[WarNox]

There are 2 vDisks, vDisk 1 has Perferred Owner as A and Current Owner as A, vDisk 2 has Preferred Owner as B and Current Owner as B. So from the SAN's perspective there doesn't seem to be an issue.

Therefore I'm assuming hosts are accessing the LUNs on Controller B via the intra-controller link?

[Torsten. · Accepted solution]

From SMU User Guide:

In both virtual and linear storage, if the owning controller fails, the partner controller assumes temporary ownership
of disk groups and resources owned by the failed controller. If a fault-tolerant cabling configuration and appropriate
mapping is used to connect the controllers to hosts, LUNs for both controllers are accessible through the partner
controller so I/O to volumes can continue without interruption.

[WarNox]

Ok, so that's pretty much in line with what I'm seeing.

I guess the next question is whether a vDisk (LUN) can be access via the partner controller and the owner at the same time?

To explain, let's say Controller B is the preferred/current owner of LUN2 but it's FC ports are disconnected, Host 1 will be able to access that LUN via Controller A. If you then plug the FC ports of Controller B into an FC switch with misconfigured zoning or some fault, will Host 1 lose access to the LUN? Because the FC ports on Controller B will now show as 'Up', even though there won't be a path to Host 1 via this faulty switch.

Thanks again.

[Torsten.]

Most drivers "ping" the pathes, so they "know" what can be used.

Even if you access a LUN owned by controller A via controller B, the driver and the array may decide after a while it could be better to transfer ownership to B.

Normally, let's say LUN1 owned by A, LUN2 owned by  B, all servers will access LUN1 via A and LUN2 via B (according to ALUA rules).

[WarNox]

Alright, so expanding on the 'ping'. Will the controller make sure it can access the hosts before using the path, rather than just checking the port state ('up' or 'down')?

[Torsten.]

The host will check if the controllers are accessible (from the host), no matter what the array ports say. The array is also aware of the host, by the way (can see the host).

[WarNox]

Cool, thanks for your help.